System and method for facilitating sensor and monitor communication

ABSTRACT

Embodiments disclosed herein may include an adapter which is capable of converting signals from an oximeter sensor such that the signals are readable by an oximeter monitor. In an embodiment, the adapter is capable of converting signals relating to calibration information from the oximeter sensor. The calibration information may relate to wavelengths of light emitting diodes within the oximeter sensor. In a specific embodiment, the adapter will convert wavelength calibration information in a first form relating to data values stored in a digital memory chip to a second form relating to a resistance value of an expected resistor within the oximeter sensor.

CROSS-REFERENCE TO RELATED APPLICATION

This claims the benefit of U.S. Provisional Patent Application No.61,072,598, filed Mar. 31, 2008, which is hereby incorporated byreference herein in its entirety.

BACKGROUND

The present disclosure relates generally to pulse oximetry and, morespecifically, to an adapter for connecting oximeter sensors withoximeter monitors.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of disclosed embodiments,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentdisclosure. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

In the field of healthcare, caregivers (e.g., doctors and otherhealthcare professionals) often desire to monitor certain physiologicalcharacteristics of their patients. Accordingly, a wide variety ofmonitoring devices have been developed for monitoring many suchphysiological characteristics. These monitoring devices often providedoctors and other healthcare personnel with information that facilitatesprovision of the best possible healthcare for their patients. As aresult, such monitoring devices have become a perennial feature ofmodern medicine.

One method for monitoring physiological characteristics of a patient iscommonly referred to as pulse oximetry, and the devices built based uponpulse oximetry methods are commonly referred to as pulse oximeters.Pulse oximeters may be used to measure and monitor various blood flowcharacteristics of a patient. For example, a pulse oximeter may beutilized to monitor the blood oxygen saturation of hemoglobin inarterial blood (SpO₂), the volume of individual blood pulsationssupplying the tissue, and/or the rate of blood pulsations correspondingto each heartbeat of a patient. In fact, the “pulse” in pulse oximetryrefers to the time-varying amount of arterial blood in the tissue duringeach cardiac cycle.

In general, monitoring systems, such as pulse oximetry systems, includea sensor and a monitor. The sensor collects data that is transmitted tothe monitor for analysis. For example, pulse oximeters typically utilizea non-invasive sensor that is placed on or against a patient's tissuethat is well perfused with blood, such as a patient's finger, toe,forehead or earlobe. The pulse oximeter sensor emits light andphotoelectrically senses the light after passage through the perfusedtissue. The sensor then transmits data relating to the sensed light tothe monitor. The light emitted by the sensor is typically selected toinclude one or more wavelengths that are absorbed or scattered in anamount related to the presence of oxygenated versus de-oxygenatedhemoglobin in the blood. Thus, data collected by the sensor relating todetected light may be used by a pulse oximeter to calculate one or moreof the above-referenced physiological characteristics based upon theabsorption or scattering of the light. For example, a monitor may use adetermination of the amount of light absorbed and/or scattered, asdetected by the sensor, to estimate an amount of oxygen in the tissueusing various algorithms.

The sensors and monitors of typical monitoring systems, such as pulseoximeter systems, are often specifically configured to communicate withone another. For example, a sensor may be specifically configured tooperate with a particular type of monitor. Indeed, if a sensor and amonitor are not specifically designed to cooperate, they may notfunction together. This can be an issue when upgrades are available fora sensor or monitor. For example, it may be desirable to utilize a newsensor that includes upgraded technology because it provides betterperformance and the upgraded technology is more affordable. However,older monitors, which can be expensive to replace, may not be able totake advantage of the improved sensor technology because they are notcompatible with the updated technology.

SUMMARY

Certain aspects commensurate in scope with this disclosure are set forthbelow. It should be understood that these aspects are presented merelyto provide the reader with a brief summary of certain embodiments of thedisclosure and that these aspects are not intended to limit the scope ofembodiments of the disclosure. Indeed, embodiments of the disclosure mayencompass a variety of aspects that may not be set forth below.

According to an embodiment, there may be provided an adapter includingcommunications circuitry configured to facilitate communication with anoximeter sensor, communications circuitry configured to facilitatecommunication with an oximeter monitor, and calibration circuitryconfigured to receive calibration information in a first form from theoximeter sensor and to convert the calibration information into a secondform which is readable by the oximeter monitor.

According to an embodiment, there may also be provided a pulse oximetrysystem including an oximeter sensor, an oximeter monitor, and an adapterconfigured to receive calibration information in a first form from theoximeter sensor and to convert the calibration information into a secondform which the oximeter monitor is capable of reading.

Finally, according to an embodiment, there may be provided a method forcommunicating calibration information from an oximeter sensor to anoximeter monitor including determining a type of calibration elementpresent within the oximeter sensor, enabling calibration signalconversion circuitry within the adapter if the calibration element is adigital memory chip, and sending a message to the oximeter monitor tobegin receiving oximetry data from the oximeter sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of this disclosure maybecome better understood when the following detailed description ofcertain exemplary embodiments is read with reference to the accompanyingdrawings in which like characters represent like parts throughout thedrawings, wherein:

FIG. 1 is a perspective view of a pulse oximetry system in accordancewith an embodiment;

FIG. 2 is a block diagram of a pulse oximeter monitor, adapter, andsensor in accordance with an embodiment;

FIG. 3 is a block diagram of a pulse oximeter monitor, adapter, andsensor incorporating LED and oximetry signal conversion circuitry inaccordance with an embodiment;

FIGS. 4A and 4B are block diagrams of a pulse oximeter sensor andadapter in accordance with an embodiment; and

FIG. 5 is a flowchart illustrating a method for initializing the signalconversion circuitry of an oximeter adapter in accordance with anembodiment.

While the present disclosure is susceptible to various modifications andalternative forms, specific exemplary embodiments thereof have beenshown in the drawings and are herein described in detail. It should beunderstood, however, that the description herein of specific exemplaryembodiments is not intended to limit the disclosure to the particularforms disclosed herein, but to the contrary, this disclosure is to coverall modifications and equivalents as defined by the appended claims.

DETAILED DESCRIPTION

Various embodiments will be described below. These described embodimentsare only exemplary of the present disclosure. Additionally, in an effortto provide a concise description of these exemplary embodiments, allfeatures of an actual implementation may not be described in thespecification. It should be appreciated that in the development of anysuch actual implementation, as in any engineering or design project,numerous implementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

The present methods and systems generally relate to physiologicalmonitoring instruments and, in particular, to systems and devices thatcooperate with sensors that include a mechanism for storing andproviding a monitor with data relating to measurement of a physiologicalcharacteristic. Embodiments of the present disclosure may include pulseoximetry sensors that include coded information relating to use of thesensors (e.g., a value associated with interpreting data from thesensor). Pulse oximetry systems are discussed below as examples tofacilitate detailed discussion of present embodiments. However, themethods and systems discussed below are merely examples, and presentembodiments are not limited to pulse oximetry devices. Indeed, someembodiments may be extended to various other physiological monitoringinstruments.

In accordance with an embodiment, blood oxygen saturation, commonlydenoted as SpO₂, may be estimated as a ratio of oxygenated hemoglobin(HbO₂) to deoxygenated hemoglobin (Hb) present in a patient's tissue.Hemoglobin is the component of blood which transports oxygen throughoutthe body. The ratio of HbO₂ to Hb can be determined by shining light atcertain wavelengths into a patient's tissue and measuring the absorbanceof the light. In an embodiment, a first wavelength may be selected at apoint in the electromagnetic spectrum where the absorption of HbO₂differs from the absorption of reduced Hb, and a second wavelength maybe selected at a different point in the spectrum where the absorption ofHb and HbO₂ differs from those at the first wavelength. For example,wavelength selections for measuring normal blood oxygenation levelstypically include a red light emitted at approximately 660 nm and anear-infrared light emitted at approximately 900 nm.

One method for estimating SpO₂ is to calculate a characteristic known asthe ratio-of-ratios (Ratrat) of the absorption of red light (RED) tonear-infrared light (IR). While various methods may be utilized tocalculate Ratrat, in one method in accordance with an embodiment, asensor is used to emit red and near-infrared light into a patient'stissue and detect the light that is reflected back. Signals indicativeof the detected light are conditioned and processed to generateplethysmographic waveforms having generally sinusoidal shape, havingboth an alternating current (AC) and a direct current (DC) component.The AC and DC components of the RED wavelength and IR wavelength signalsmay then be used to calculate Ratrat, which has been observed tocorrelate well to SpO₂. This observed correlation may be used toestimate SpO₂ based on the measured value of the Ratrat.

Therefore, pulse oximeters may precisely measure Ratrat in order todetermine SpO₂. The relationship between Ratrat and SpO₂ may follow asmooth line that serves as a sensor calibration curve. Because the lightabsorption of the blood's HbO₂ and Hb is significantlywavelength-dependent, the relationship between Ratrat and SpO₂ maydepend heavily upon the specific wavelength emissions of the sensor'slight emitting diodes (LEDs). For instance, if the red LED emits at 640nm as opposed to 660 nm, the light absorption of the blood may increasecompared to a truly red emitter. The result may be that the sensor'scalibration curve would be shifted and rotated to a certain degree.

Therefore, more accurate measurements of SpO₂ may be taken when thesensor's calibration curve corresponds to the actual wavelengths of thesensor's LEDs. For this reason, pulse oximeter manufacturers mayidentify the emitted wavelengths in order to achieve accurate readings.Many manufacturers identify an LED wavelength range for a particularsensor and program a corresponding calibration curve into a pulseoximetry monitor that corresponds to this LED wavelength range. To doso, these manufacturers may use a resistor-encoding scheme in whichseveral calibration curves are programmed into pulse oximeters to span abroad range of LED wavelengths.

This resistor calibration method, which may be abbreviated as RCAL™ insystems manufactured by the present assignee, communicates to themonitor which curves should be used. When the sensor is connected to themonitor, a resistor within the sensor may be read by the monitor toidentify specifically which of the pre-programmed curves should be usedto calculate SpO₂ values. During the manufacturing of each sensor, thewavelength characteristics of the red and infrared LEDs may be measuredand an appropriate resistor may be installed in the sensor. The RCAL™system may be used by the monitor to identify from a lookup table (e.g.,Table 1) which of the pre-programmed curves should be used based on thespecific resistor values.

TABLE 1 Example RCAL ™ Lookup Values RCAL ™ Resistor (Ω) CalibrationCurve 1000 Curve #1 2000 Curve #2 3000 Curve #3 . . . . . . N,000  Curve#N

However, predefining calibration curves to address LED wavelengthvariations can be an issue for several reasons. First, pulse oximetrymanufacturers may not be able to take advantage of newer high-efficiencyLEDs because their spectral properties may be different from thosedesigned by semiconductor companies years ago. Newer LEDs can reducepower needs of oximeters, leading to longer battery life. In addition,newer LEDs can dramatically increase signal strength, improvingmonitoring performance. Therefore, as newer LEDs become available,oximeter manufacturers may want to be able to take advantage of thelatest advancements in LED technology. Second, oximeter manufacturersmay be constrained and unable to implement new sensor designs when thenew designs do not precisely conform to the pre-programmed calibrationcurves in the monitors. Having to fit new sensors into the availablechoices of calibration curves may limit the possibilities for new sensordesigns. Finally, many RCAL™ calibration curves were created in themid-1980s, based on LEDs and sensor designs of that time. New sensorsdeveloped since then have had to conform to these pre-programmed curvesto ensure compatibility across the installed base of oximeter monitors.

In response to these issues, new oximeter systems have been developed toprovide for greater sensor and monitor performance while at the sametime accommodating future sensor designs as patient care evolves. Onesuch system accomplishes these objectives by incorporating a smalldigital memory chip within the sensor. Each digital memory chip may beprogrammed with the full calibration information for that sensor, alongwith any other sensor-specific data the oximeter can use to enhanceperformance. This design allows manufacturers to develop sensors thataddress specific clinical needs without being hampered by the earliersensor calibration constraints.

This type of system still utilizes calibration. However, instead ofhaving to fit within the pre-programmed curves within oximeter monitors,sensors with digital memory chips may hold their individual calibrationcurves in memory. As such, each sensor may be programmed with specificcoefficients which define its calibration curve. Therefore,manufacturers can now store within the chip any calibration curveneeded, whether for current sensor designs or for those created in thefuture. Because new calibration curves can be developed as needed,manufacturers can design new sensors with improved performance withoutthe constraints of the past.

Though existing oximeter monitors could conceivably be re-programmedwith additional curves, the process for doing so could prove verydifficult, particularly when the large numbers of installed monitorsaround the world is taken into account. Building digital memory chipswithin sensors allows for integrating new sensor calibration curveswithout the hassle of updating oximeter monitors. Therefore,implementing upgrades through sensors, rather than monitors, may provemore cost effective and efficient.

In addition, the memory chip may provide room for additionalsensor-specific operating parameters to be stored within the sensor. Forexample, the model name of the sensor being stored, and model-specifictroubleshooting tips may be provided. However, despite all of theadvantages created by building a memory chip into the sensors, one majordisadvantage may be created—the fact that oximeter monitors may notinherently be able to communicate with the sensors. Indeed, whereasolder monitors may be expecting an encoded signal via a resistor, theymay now be interfacing with a chip holding the calibration curve inmemory. Conversely, when newer monitors are expecting to interface witha memory chip, they may experience only a resistor element in an oldersensor. Therefore, it is now recognized that it would be advantageous tohave an adapter which can modify the sensor signals accordingly.

FIG. 1 is a perspective view of a pulse oximetry system in accordancewith an embodiment. The pulse oximetry system is generally indicated byreference numeral 100. The system 100 may include a sensor 110, anadapter 120, and a monitor 130 which cooperate to detect and analyzepatient characteristics. In the illustrated embodiment, the monitor 130couples via the adapter 120 to the sensor 110 that is applied to apatient 140. More specifically, the sensor 110 may be configured todetect and transmit signals to the monitor 130 via the adapter 120. Thesignals transmitted by the sensor 110 may be indicative of SpO₂ levelsin the patient's 140 tissue. The adapter 120 may convert the signalsfrom the sensor 110 into a form that is readable by the monitor 130. Forexample, the monitor may be configured to receive information from thesensor 110 relating to a resistance value (for calibration purposes)whereas the sensor 110 may be configured to transmit information to themonitor 130 relating to values read from a memory feature of the sensor110.

In the illustrated embodiment, the sensor 110 includes a pair of LEDs112, a photo detector 114, a sensor cable 116, and a sensor connectingplug 118. In FIG. 1, the sensor 110 is shown as a clip-on sensor.However, present embodiments can be applied to many sensorimplementations, including those attached to a patient by adhesive andother attachment means. Light from the LEDs 112 at two differentwavelengths (e.g., red and infrared) may be transmitted through apatient's blood perfused tissues (e.g., in a finger) and detected by thephoto detector 114. Selection of the wavelengths of the LEDs 112 may bebased on a number of factors. Such factors may include the absorptioncharacteristics of the patient and transmission medium. The detectedoptical signal from the photo detector 114 may then be provided to themonitor 130 for processing.

The sensor 110 may be connected to the sensor cable 116. In theillustrated embodiment, the sensor cable 116 is directly connected tothe adapter 120 via the sensor connecting plug 118. However, as will beappreciated by those in the art, the sensor 110 may also be connecteddirectly to the monitor 130 (e.g., in instances where the sensor 110 iscompatible with the monitor 130). In addition, in other embodiments, thesensor 110 may be configured to connect wirelessly with the adapter 120and/or the monitor 130, obviating the need for the sensor cable 116 andsensor connecting plug 118.

Also, in the illustrated embodiment, the adapter 120 includes an adapterbody 122, an adapter-to-sensor connecting plug 124, an adapter cable126, and an adapter-to-monitor connecting plug 128. The adapter body 122may contain all of the circuitry required to convert the signals fromthe sensor 110 into a form that is readable by the monitor 130. Theadapter 120 may be directly connected to the sensor 110 via theadapter-to-sensor connecting plug 124 and adapter cable 126. Similarly,the adapter may be connected to the monitor 130 via theadapter-to-monitor connecting plug 128 and adapter cable 126. Inaddition, in other embodiments, the adapter 120 may be configured toconnect wirelessly with the sensor 110 and/or the monitor 130, obviatingthe need for the adapter cable 126 and adapter connecting plugs 124,128. Also, the adapter 120 may have a self-contained power source (e.g.,rechargeable battery) within the adapter body 122, plug into a poweroutlet directly (using electrical cords not shown), or derive its powerfrom the monitor 130.

In the illustrated embodiment, the monitor 130 may be a pulse oximeter,such as those available from Nellcor Puritan Bennett LLC and/orCovidien, or may be another monitor for measuring other body-relatedmetrics using spectrophotometric and/or other methods. Additionally, themonitor 130 may be a multi-purpose monitor suitable for performing pulseoximetry and measurement of other combinations of physiological and/orbiochemical monitoring processes, using data acquired via the sensor110.

The adapter 120 has been described for use in combination with a sensor110 and a monitor 130 wherein the monitor 130 performs the signalprocessing of the detected signal and compression of the processed data.In another embodiment, the adapter 120 may be configured to process (andcompress, if necessary or desirable) the detected signal. Thisembodiment allows for independent operation of the sensor 110 andadapter 120 without support from a monitor 130. The data stored withinthe sensor 110 and adapter 120 may be provided to a monitor 130 fordisplay. The amount of signal processing and compression that can beachieved by circuitry within the adapter 120 may be primarily limited bythe available technology, which inevitably improves over time. In thenear term, physiological data that does not require extensive signalprocessing and compression (e.g., temperature, peak amplitude in awaveform, heart rate, and so on) can be collected and stored by theadapter 120.

FIG. 2 is a block diagram of a pulse oximeter system incorporating acalibration element 202 within the sensor 110 in accordance with anembodiment. In one embodiment, the calibration element 202 may be atwo-lead semiconductor digital memory chip. The calibration element 202may be part of the sensor 110 which also includes red and infrared LEDs206, along with a photo detector 208. If desired, the LEDs 206 may bereplaced with other light emitting elements such as lasers.

The oximeter monitor 130 may include a read circuit 210, a drive circuit212, lookup tables 214 and 216, a controller 218, an amplifier 220, afilter 222, and an analog-to-digital converter 224. The read circuit 210may be provided for reading multiple coded values across the two leads226, 228 connected to the adapter calibration circuitry 270 which may inturn be connected to the calibration element 202 via two other leads230, 232. One value may be provided to a lookup table 214 to determineappropriate wavelength-dependent coefficients for the oxygencalculation. The other value(s) may then be provided to another lookuptable(s) 216 which provides input (e.g., coefficients) to othercalculations performed by the controller 218. The controller 218 mayprovide signals to a drive circuit 212 to control the amount of drivecurrent provided to the LEDs 206.

The photo detector 208 may be connected through the amplifier 220 andthe filter 222 to the A/D converter 224. This forms a feedback path usedby the controller 218 to adjust the drive current to optimize theintensity range of the signal received. For example, the signal may bewithin the analog range of the circuits employed. The signal may also bewithin the range of the A/D converter 224. For example, one rule thatmay be applied is to adjust LED drives and amplifier gains so that bothred and IR signals fall between 40% and 80% of full scale reading of theA/D converter 224.

If the sensor 110 is the type that uses the RCAL™ calibration method,leads 226 and 228 of the sensor 110 may be connected directly to leads230 and 232 of the monitor 130. As such, after connecting the sensor 110to the monitor 130, the read circuit 210 may read an analog voltagewhich corresponds to the RCAL™ resistor value of the sensor 110. Thisvoltage may then be applied to an A/D converter (not shown) to provide avalue which can be used to index into the lookup table 214. Conversely,certain issues may arise if the monitor 130 is configured to communicatewith a sensor 110 which uses the RCAL™ calibration method but, instead,the sensor 110 uses a digital memory chip for calibration purposes.

However, in an embodiment, the adapter 120 contains adapter calibrationcircuitry 270 which is connected between the pairs of leads 226, 228 and230, 232. As such, the adapter calibration circuitry 270 may beresponsible for converting signals sent to/from the read circuit 210such that both older sensors (using resistors for calibration) and newersensors (using digital memory chips for calibration) may be compatiblewith monitors configured to operate with sensors that use resistors forcalibration. As will be appreciated by one skilled in the art, themethods described below for implementing an adapter 120 may also beapplied to other situations. More specifically, similar methods may beused within the adapter calibration circuitry 270 such that both oldersensors (using resistors for calibration) and newer sensors (usingdigital memory chips for calibration) may be compatible with monitorsconfigured to connect to sensors which use digital memory chips forcalibration. In either case, signals sent to/from the read circuit 210may be converted from a first form to a second form with which themonitor 130 is configured to operate.

One objective of the adapter calibration circuitry 270 is to ensure thatthe monitor 130 responds in the same manner when either type ofsensor—one that uses a resistor for calibration or one that uses amemory chip for calibration—is in communication with the monitor 130 viathe adapter 120. This can be accomplished using any number of methodsand features, a few of which will be described below. However, it shouldbe understood that these disclosed embodiments are not intended to belimited to the particular methods and features disclosed below.

FIG. 3 is a block diagram of a pulse oximeter system incorporating LEDand oximetry signal conversion circuitry 310, 320 in accordance with anembodiment. In addition to converting signals relating to sensorcalibration, the adapter 120 may also be used for conversion of LEDsignals to the sensor 110 and oximetry signals from the sensor 110. Forinstance, in response to information gathered from the memory chip inthe sensor 110 (e.g., either calibration information or any otherinformation stored in the memory chip), either the LED signals orreturning oximetry signals may be modified and/or pre-conditioned totake into account particular characteristics of the sensor 110. Inaddition, the adapter LED conversion circuitry 310 and/or the oximetrysignal conversion circuitry 320 may simply be used to offload some ofthe functionality of the monitor 130, depending on the circumstances.

FIGS. 4A and 4B are block diagrams of the adapter 120 and the sensor 110in accordance with various embodiments. In these embodiments, theadapter calibration circuitry 270 may contain switches 402, 404 enablingtwo alternate modes of operation for the adapter 120. FIG. 4Aillustrates the first mode of operation, where the adapter 120 isconnected to the sensor 110 employing a resistor-based calibrationelement 410. In this situation, there is no need to use the calibrationsignal conversion circuitry 420. Therefore, it may be bypassed and thesignal from the resistor-based calibration element 410 may simply bepassed along through the adapter calibration circuitry 270 to themonitor 130. Conversely, FIG. 4B illustrates the second mode ofoperation, where the adapter 120 is connected to the sensor 110employing a memory chip-based calibration element 430. In thissituation, the calibration signal conversion circuitry 420 is neededand, therefore, should not be bypassed. In both situations, initial readcircuitry 440 will most likely be used to ensure that switches 402, 404are toggled appropriately upon connecting the sensor 110, the adapter120, and the monitor 130 so that the read circuit 210 of the monitor 130is able to process the signals returned by the sensor 110 via theadapter 120.

FIG. 5 shows an embodiment of a method for initializing the calibrationsignal conversion circuitry 420 of the adapter 120. Initially, themonitor 130, the adapter 120, and the sensor 110 may be connected to oneanother, as indicated by block 502. Upon detecting connection, theinitial read circuitry 440 may toggle the switches 402, 404 (block 504)to bypass the calibration signal conversion circuitry 420. Clearing theconnection between the adapter 120 and the sensor 110 allows for theinitial read circuitry 440 to interrogate (block 506) the sensor 110 inorder to establish what type of calibration element 202 is being used bythe sensor 110.

At this point, a determination may be made (block 508) by the initialread circuitry 440 of whether a memory chip is used in sensor 110 forcalibration purposes. This may be determined, for instance by attemptingto access a particular value from a memory chip. If the value isreturned, the memory chip is being used. If the sensor 110 is, in fact,using a memory chip, the initial read circuitry 440 may toggle theswitches 402, 404 to enable the calibration signal conversion circuitry420, as indicated by block 510. If the sensor 110 is not using a memorychip, it may be assumed that a resistor is being used and the step ofenabling the calibration signal conversion circuitry 420 may not beperformed. Regardless, once the switches 402, 404 are in the correctlocation and the calibration signal conversion circuitry 420 has beenappropriately enabled or bypassed, the initial read circuitry 440 maysend a message to the read circuit 310 of the monitor 130 that it canproceed collecting oximetry information from the sensor 110 via theadapter 120, as indicated by blocks 512 and 514.

Therefore, once it has been determined that the sensor 110 is using amemory chip for calibration, the calibration signal conversion circuitry420 may convert signals received from the memory chip within the sensor110 so that the monitor 130 can operate in the same manner as if it wereconnected directly to a sensor using a resistor for calibration. Again,this can be accomplished using any number of methods, a few of whichwill be described below. However, it should be understood that thedisclosed embodiments are not intended to be limited to the particularmethods disclosed below.

In an embodiment, the calibration signal conversion circuitry 420 maycontain an inverse lookup table, essentially mimicking all of the lookupvalues listed above in Table 1 and inverting them, as shown in Table 2.To use this method, the initial read circuitry 440 may obtain thecalibration curve from the memory chip in the sensor 110 and use thiscurve as an index to lookup the corresponding RCAL™ resistor value.Then, the initial read circuitry 440 may send an analog voltage to theread circuit 210 of the monitor 130 corresponding to the RCAL™ resistorvalue. To do this, the adapter 120 may be pre-programmed with an updatedinverse lookup table corresponding to the lookup values used by themonitor 130. Alternatively, upon connection of the monitor 130 and theadapter 120, the calibration signal conversion circuitry 420 couldinterrogate the lookup table used by the monitor 130 and synchronize thevalues in the adapter's 120 inverse lookup table accordingly. In thismanner, the inverse lookup table may function properly withoutpre-programming the inverse lookup table into the adapter 120 at thetime the adapter 120 is manufactured.

TABLE 2 Example Inverse Lookup Values Calibration Curve RCAL ™ Resistor(Ω) Curve #1 1000 Curve #2 2000 Curve #3 3000 . . . . . . Curve #NN,000 

In another embodiment, the calibration signal conversion circuitry 420may contain an actual series of resistors that can be switched on andoff to create a combined resistance through the calibration signalconversion circuitry 420 approximating the RCAL™ resistance that wouldhave been used if the sensor 110 used a resistor for calibrationpurposes. This method may obviate the need for converting the signalsent to the read circuit 210 since there would be an actual resistancevalue in place. In other words, using this method, the calibrationsignal conversion circuitry 420 may physically recreate the resistancethat would have been used if the sensor used a resistor for calibrationpurposes.

While the subject of this disclosure may be susceptible to variousmodifications and alternative forms, specific embodiments have beenshown by way of example in the drawings and have been described indetail herein. However, it should be understood that this disclosure isnot intended to be limited to the particular forms disclosed. Rather,this disclosure is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of this disclosure asdefined by the following appended claims.

1. An adapter, comprising: communications circuitry capable of facilitating communication with an oximeter sensor; communications circuitry capable of facilitating communication with an oximeter monitor; and calibration circuitry capable of receiving calibration information in a first form from the oximeter sensor and converting the calibration information into a second form which is readable by the oximeter monitor.
 2. The adapter of claim 1, wherein the calibration information generally relates to the wavelengths of light emitting diodes within the oximeter sensor.
 3. The adapter of claim 1, wherein the first form generally relates to data values stored in a digital memory chip within the oximeter sensor.
 4. The adapter of claim 1, wherein the second form generally relates to a resistance value of an expected resistor within the oximeter sensor.
 5. The adapter of claim 1, wherein the calibration circuitry is configured to convert the calibration information based on values from an inverse lookup table.
 6. The adapter of claim 1, wherein the calibration circuitry is configured to convert the calibration information using a series of resistors and switches.
 7. The adapter of claim 1, comprising circuitry configured to convert light emitting diode signals to and from the oximeter sensor and oximeter monitor.
 8. The adapter of claim 1, comprising circuitry configured to convert signals detected by a photo detector within the oximeter sensor.
 9. The adapter of claim 1, wherein the adapter is configured to wirelessly communicate with the oximeter sensor.
 10. The adapter of claim 1, wherein the adapter comprises an independent power source.
 11. A pulse oximetry system, comprising: an oximeter sensor; an oximeter monitor; and an adapter capable of receiving calibration information in a first form from the oximeter sensor and converting the calibration information into a second form which the oximeter monitor is capable of reading.
 12. The pulse oximetry system of claim 11, wherein the adapter is configured to switch between a first mode in which the calibration information is converted from the first form to the second form and a second mode in which the calibration information is not converted from the first form.
 13. The pulse oximetry system of claim 11, wherein the oximeter sensor comprises at least one light emitting diode, at least one photo detector, and a digital memory chip capable of storing various data regarding the oximeter sensor.
 14. The pulse oximetry system of claim 11, wherein the oximeter sensor and the adapter are configured to wirelessly communicate with each other.
 15. The pulse oximetry system of claim 11, wherein the adapter comprises circuitry configured to convert light emitting diode signals to and from the oximeter sensor and oximeter monitor.
 16. The pulse oximetry system of claim 11, wherein the adapter comprises circuitry configured to convert signals detected by a photo detector within the oximeter sensor.
 17. A method for communicating calibration information from an oximeter sensor to an oximeter monitor, comprising: determining a type of calibration element present within the oximeter sensor; enabling calibration signal conversion circuitry within the adapter if the calibration element is a digital memory chip; and sending a message to the oximeter monitor to begin receiving oximetry data from the oximeter sensor.
 18. The method of claim 17, comprising converting signals from the oximeter sensor relating to values stored in the digital memory chip into signals corresponding to expected resistance values.
 19. The method of claim 17, comprising bypassing the calibration signal conversion circuitry before determining the type of calibration element present within the oximeter sensor.
 20. The method of claim 19, comprising bypassing the calibration signal conversion circuitry via electrical switches. 